Aromatic copolyamides, process for preparing them and their use for the production of shaped structures

ABSTRACT

Aromatic copolyamides, process for preparing them and their use for the production of shaped structures 
     Aromatic copolyamide which is soluble in organic solvents, and a process for its preparation, which contains the recurring structural units (I), (II) and (III) ##STR1## to the extent of at least 90 mol % and 0 to 5 mol % of end groups of the structural units (IV) ##STR2## The sum of the molar proportions of (II) and (III) is in the ratio of 0.9:1 to 1.1:1 to the molar proportion of (I), and at the same time the molar proportions of (II) and (III) are in a ratio to one another of 60:40 to 10:90. 
     The copolyamides are suitable for the production of shaped articles or for coatings and for the production of fibers, membranes and films.

DESCRIPTION

Aromatic copolyamides, process for preparing them and their use for theproduction of shaped structures. This application is a 371 ofPCT/EP92/00392 filed Feb. 25, 1992.

Aromatic polyamides are known as materials of high mechanical, chemicaland heat stability. Fibers and films of these materials exhibit highstrengths and high initial moduli (modulus of elasticity), which rendersthem particularly suitable for industrial fields of use, for example forreinforcing plastics or as filter materials.

Such polymers are usually prepared by reaction of aromatic diamines witharomatic dicarboxylic acid chlorides in aprotic organic solvents of theamide type, for example N,N-dimethylacetamide (DMAc) orN-methylpyrrolidone (NMP), alkali metal chlorides or alkaline earthmetal chlorides being added, if appropriate, to improve the solubilityand the hydrogen chloride formed subsequently being neutralized, forexample with calcium oxide (DE-A-19 29 713, DE-B-22 19 703).

However, the preparation and processing of such polyamides proves to bevery expensive. Because of its poor solubility in organic solvents, evenin the presence of organic salts, such as lithium chloride or calciumchloride, as solubilizing agents, the polymer already precipitates outof the reaction medium shortly after its formation. It must be isolated,washed and dried, and then dissolved again in a solvent suitable for theprocessing.

These polymers are preferably spun from concentrated sulfuric acid, butthis causes particular problems in handling (work safety, corrosion) anddisposal.

Sparingly soluble polyamides, such as poly(p-phenyleneterephthalamide),have bonds arranged in parallel or coaxially to one another startingfrom the aromatic units. To achieve better solubility, it is possible toemploy comonomers which are intended to serve to interrupt the parallelor coaxial pattern of bonds along the polymer chains.

Aromatic copolyamides of terephthalic acid, p-phenylenediamine and3,4'-diaminodiphenyl ether can be processed from the NMP solutionsobtained during the preparation process to give fibers and films havinggood strengths. However, synthesis of 3,4'-diaminodiphenyl ether andpurification thereof are very expensive because of the asymmetricstructure. Modifications of poly(p-phenylene-terephthalamide) which areindustrially simpler, for example by incorporation of meta-linkage units(for example m-phenylenediamine) result in a deterioration in themechanical properties (DE-B-30 07 063).

It is furthermore known that polyamides of p-phenylenediamine and2,5-furandicarboxylic acid derivatives can be processed from NMP withaddition of lithium chloride to give fibers and films (EP-A-0 256 606).In this process, the monomers are polymerized with one another directlyin the presence of phosphorous acid triphenyl ester and pyridine. Theresulting polymers have intrinsic viscosities of more than 1.5 dl/g(measured at 30° C. in 98% strength sulfuric acid).

An alternative synthesis process for the preparation ofpoly(p-phenylene-2,5-furandicarboxamide) which is achieved withoutadditions which are ecologically unacceptable or are often regarded astoxic, such as phosphorus compounds or pyridine, is described in PolymerCommunications, 26, 246-249 (1985). However, in contrast to the productsobtained by a direct polycondensation, the products obtained by thisroute have considerably lower intrinsic viscosities.

The present invention is therefore based on the object of discovering anaromatic copolyamide which has comparably good mechanical properties topoly(p-phenylene-terephthalamide), has a very good solubility in organicsolvents and can be processed directly from these solutions to givehigh-quality fibers and films; whereby the process for the preparationof these polyamides should be economically and ecologically favorableand readily accessible diamines and dicarboxylic acid derivatives shouldbe employed as starting substances.

The object is achieved by the present invention. The invention relatesto an aromatic copolyamide which is soluble in organic solvents andcontains the recurring structural units (I), (II) and (III) ##STR3## tothe extent of at least 90 mol % and 0 to 5 mol % of end groups of thestructural units (IV) ##STR4## The symbols Ar¹, Ar² and R¹ have thefollowing meaning: Ar¹ is a divalent C₁ --C₄ aromatic radical which issubstituted by optionally one or two branched or unbranched C₁ --C₄--alkyl or C₁ --C₄ --alkoxy radicals, aryl or aryloxy radicals or isunsubstituted and is optionally bridged by --SO₂ -- or --CO--, the aminegroups being on non-adjacent ring carbon atoms,

Ar² is a divalent aromatic radical which is substituted by optionallyone or two branched or unbranched C₁ --C₄ --alkyl or alkoxy radicals,aryl or aryloxy radicals or C₁ --C₆ --perfluoroalkyl or perfluoroalkoxyradicals or by fluorine, chlorine or bromine or is unsubstituted.

Ar¹ and Ar² independently of one another can be identical or different.

R¹ is an optionally halogen-substituted C₁ --C₁₀ --alkyl group or aradical of the structure (V) ##STR5## in which R² is hydrogen or halogenor a branched or unbranched alkyl or alkoxy radical or an aryl oraryloxy radical. The sum of the molar proportions of (II) and (III) tothe molar proportion of (I) here are in the ratio of 0.9:1 to 1.1:1, themolar proportions of (II) and (III) simultaneously being in a ratio toone another of 60:40 to 10:90.

The following compounds are suitable for the preparation of thecopolyamides according to the invention:

a.) diamine derivatives of the formula (VI)

    H.sub.2 N--Ar.sup.1 --NH.sub.2                             (VI)

such as, for example,

para-phenylenediamine

2-methyl-para-phenylenediaminebenzidine

3,3'-dimethylbenzidine

naphthylene-2,6-diamine

4,4'-diaminodiphenyl ether

1,4-bis-(4-aminophenoxy)-benzene

1,4-bis- (4-aminophenylisopropyl)-benzene

4,4'-diaminodiphenyl sulfone

b. ) dicarboxylic acid derivatives of the formula (VII) ##STR6## inwhich X is a hydroxyl group or chlorine.

Compounds of the formula (VII) include, for example,

terephthalic acid

terephthalic acid dichloride

isophthalic acid

isophthalic acid dichloride

2-chloroterephthalic acid

2-chloroterephthalic acid chloride

naphthalene-2,6-dicarboxylic acid

naphthalene-2,6-dicarboxylic acid chloride

dicarboxylic acid chlorides preferably being used, and

c.) furandicarboxylic acid derivative of the formula (viii) ##STR7##

(X has the abovementioned meaning)

Examples of compounds of the formula (VIII) are:

2,5-furandicarboxylic acid and

2,5-furandicarboxylic acid chloride

The preparation of the aromatic copolyamides according to the inventionis carried out by solution condensation of mixtures of (VII) and (VIII)with (VI) in known polyamide solvents. Polyamide solvents are understoodas meaning polar aprotic solvents which contain amide bonds, such as,for example, dimethylacetamide (DMAc), dimethylformamide (DMF) andlactams, such as, for example, N-methylpyrrolidone andN-methylcaprolactam. Components (VII) and (VIII) are in a molar ratio toone another of 60:40 to 10:90 in the process according to the invention,the proportion thereof, based on the proportion of component (VI), being90 to 110 mol %, preferably 100 mol %. The acid chlorides (VII) and(VIII) are preferably added to the reaction mixture as a homogenousmixture, particularly preferably as a solution of the two components insome of the solvent used for the polycondensation. Components (VI),(VII) and (VIII) are subjected to polycondensation with one another attemperatures in the range from -20° to 120° C. preferably in the rangefrom 0° to 100° C. particularly preferably in the range from 10° to 90°C. If appropriate, halide salts of metals of the first and/or secondgroup of the Periodic Table of the Elements are added to these solventsin a known manner to increase the dissolving capacity or to stabilizethe copolyamide solutions. Preferred additives are calcium chlorideand/or lithium chloride.

The terminal amino groups of the aromatic copolyamide can be neutralizedby addition of a monocarboxylic acid chloride or anhydride of theformula (IX) ##STR8## in which Y is chlorine or a group ##STR9## and

R¹ has the abovementioned meaning. Examples of such chain-terminatingagents are benzoyl chloride, fluorobenzoyl chloride, diphenylcarboxylicacid chloride, phenoxybenzoyl chloride, acetic anhydride, chloroaceticanhydride and propionic anhydride.

If appropriate, such chain-terminating agents can be substituted on thearomatic nucleus, preferably by fluorine or chlorine atoms. Benzoylchloride is preferably employed.

The polycondensation reaction is preferably carried out such that 2 to20, preferably 5 to 15%, by weight of polycondensate are present in thesolution after the reaction has ended.

The amino groups on the ends of the polymer chain are usuallyneutralized by addition of a monofunctional acid chloride or an acidanhydride of the formula (IX) when the solution of the polymer formedhas reached the desired viscosity.

In a preferred embodiment of the preparation process, an at leastequivalent amount of one or more acid-binding inorganic or organicadditives is added to the reaction mixture to neutralize the hydrogenchloride formed during the reaction. Examples of such additives arealkali metal oxides and hydroxides and alkaline earth metal oxides andhydroxides, for example lithium hydroxide and calcium oxide, andcompounds of the formulae (X), (XI) and (XII), such as propylene oxide,ammonia, triethylamine and pyridines, or pyridines which are substitutedin the 2-, 3- or 4-position. ##STR10##

R⁴, R⁵, R⁶, R⁷ and R⁸ in compounds of the formulae (X), (XI) and (XII)are identical or different and independently of one another are hydrogenor a branched or unbranched alkyl group, preferably a C₁ to C₃ alkylgroup. In the case where lithiumhydroxide, calcium oxide or ammonia isused, the neutralizing agent is preferably added only after the end ofthe polycondensation.

In another preferred embodiment, a compound of the formula (VI) and anat least equivalent amount, preferably 100 to 120 mol %, based on (VI),of one of the compounds (X), (XI) or (XII) are subjected topolycondensation with a mixture of (VII) and (VIII) and, when thepolycondensation has ended, similarly an at least equivalent amount ofan alkali metal oxide or hydroxide or alkaline earth metal oxide orhydroxide is added. In this manner, the acid-binding component (X),(XI), (XII) first added is for the most part liberated again and can berecovered again, for example by distillation.

If appropriate, suitable amounts of additives are added to thesolutions. Examples are light stabilizers, antioxidants, flameproofingagents, antistatics, dyestuffs, colored pigments or fillers. To isolatethe copolyamides, a precipitating agent can be added to the solutionsand the coagulated product can be filtered off. Examples of suitableprecipitating agents are: water, preferably with additions of acid, suchas hydrochloric acid or acetic acid, mixtures of water and aphroticsolvents, such as DMF, DMAc and NMP, and methanol.

The intrinsic viscosities (=Staudinger Index) of the copolyamides whichhave been prepared by the process according to the invention are in therange from 1.0 to 5.0 dl/g, preferably in the range from 1.0 to 3.0dl/g.

Intrinsic viscosity ([η]₀) is understood as meaning the followingrelationship: ##EQU1## ηrel=relative viscosity c=concentration of thesolution in g/dl

To prepare shaped structures from the copolyamides according to theinvention, the resulting solutions are filtered, degassed and processedin a known manner to give filaments, fibers, films, membranes orcoatings. For example, fibers can be produced by using a wet spinningunit, where the polymer solution is forced out through suitable nozzlesinto a precipitating bath and the resulting filaments are drawn throughwashing baths and stretched at a relatively high temperature. Suitableprecipitating baths are aqueous solutions of amide solvents, such asN-methylpyrrolidone, and may also include aqueous salt solutions, suchas calcium chloride solutions.

Stretching, in the production of filaments, fibers and films, comprisesslight wet stretching and greater contact stretching. For contactstretching, for example, the filaments are drawn over hot plates("irons") having a surface temperature in the range from 250° C. to 450°C.

EXAMPLES:

The intrinsic viscosities were measured at 25° C. in NMP with additionof 2.0% of lithium bromide.

Example 1

Aromatic copolyamide of 100 mol % of p-phenylenediamine, 50 mol % of2,5-furandicarboxylic acid chloride and 50 mol % of terephthalic aciddichloride.

A solution of 13.52 g of p-phenylenediamine (0.125 mol) and 9.2 g oflithium chloride in 175 ml of N-methylpyrrolidone (NMP) and 34.95 g of2-picoline was initially introduced into a reaction vessel of 300 mlcapacity. A solution of 12.15 g of 2,5-furandicarboxylic acid dichloride(0.063 mol) and 12.79 g of terephthalic acid dichloride (0.063 mol) in44 ml of NMP was added at a temperature of +5° C., while stirring andblanketing with a layer of N₂. All the substances had been carefullypurified and dried beforehand. The mixture was heated to 70° C. in thecourse of 30 minutes, while stirring, and subjected toafter-condensation at this temperature for 120 minutes. 0.7 g of benzoylchloride (0.005 mol) was then added and the mixture was stirred for afurther 30 minutes. The resulting solution was filtered and addeddropwise to an excess of 2% strength hydrochloric acid. The polymerwhich had precipitated was washed 4 times with water heated to 70° C.and 3 times with acetone and dried in vacuo at 120° C. for 24 hours. Theintrinsic viscosity was 2.05.

Example 2

Aromatic copolyamide of 100 mol % of p-phenylenediamine, 65 mol % of2,5-furandicarboxylic acid chloride and 35 mol % of terephthalic aciddichloride.

The polycondensation according to Example 1 was repeated with thedifference that a solution of 15.99 g of furandicarboxylic acid chloride(0.083 mol) and 9.06 g of terephthalic acid chloride (0.045 mol) in 43ml of NMP was used instead of the abovementioned solution of thesecompounds. The intrinsic viscosity of the polymer was 1.25.

Example 3

Aromatic copolyamide of 100 mol % of p-phenylenediamine, 85 mol % of2,5-furandicarboxylic acid chloride and 5 mol % of terephthalic aciddichloride.

A solution of 108.1 g of p-phenylenediamine (1.0 mol) and 73.6 g oflithium chloride in 1400 ml of NMP and 279.4 g of 2-methylpyridine (3.0mol) was initially introduced into a reaction vessel of 3 1 capacity. Asolution of 16.60 g of furandicarboxylic acid chloride (0.86 mol) and31.1 g of terephthalic acid dichloride (0.153 mol) in 327 ml ofN-methylpyrrolidone was added at a temperature of 5° C. in a nitrogenatmosphere, while stirring. All the components had been carefullypurified and dried beforehand. The mixture was heated to 70° C. in thecourse of 20 minutes, while stirring and blanketing with a layer ofnitrogen, and subjected to after-condensation at this temperature for 90minutes. 5.6 g of benzoyl chloride (0.04 mol) were then added. After afurther reaction time of 30 minutes, the polymer was isolated from theresulting solution as described under Example 1. The intrinsic viscositywas 1.06.

Example 4

Aromatic copolyamide of 100 mol % of p-phenylenediamine, 50 mol % of2,5-furandicarboxylic acid dichloride and 50 mol % of terephthalic aciddichloride.

A solution of 81.1 g of p-phenylenediamine (0.75 mol) and 81 g oflithium chloride in 2000 ml of N-methylpyrrolidone (NMP) was initiallyintroduced into a reaction vessel of 3 1 capacity. A solution of 72.37 gof 2,5-furandicarboxylic acid dichloride (0.375 mol) and 76.13 g ofterephthalic acid dichloride (0.375 mol) in 200 g of NMP was added at atemperature of 5° C., in a nitrogen atmosphere, while stirring.

The mixture was heated to 70° C. in the course of 60 minutes, whilestirring and blanketing with a layer of nitrogen, and subjected tofurther condensation at this temperature for 90 minutes. 5.6 g ofbenzoyl chloride (0.04 mol) were then added, and a suspension of 49.1 gof calcium oxide (0.90 mol) in 30 ml of NMP was added after a further 20minutes. The mixture was subsequently stirred at 70° C. for 20 minutes,filtered and degassed. The resulting solution contained 6.6% by weightof copolyamide, 3.05% by weight of lithium chloride and 3.13% of calciumchloride.

A portion of the solution was added dropwise to an excess of water. Thepolymer which had precipitated was washed 4 times with water heated to70° C. and 3 times with acetone and dried in vacuo at 120° C. for 24hours. The intrinsic viscosity was 2.71.

The remainder of the solution was wet-spun to fibers. For this, it wasspun from a nozzle with 100 openings of 0.06 mm each into a horizontallypositioned coagulation bath comprising a solution, heated to 73° C. ofNMP in water, at a rate of 16.0 m/minute. The resulting filaments weredrawn off through two water baths, a washing machine, over a dryinggodet at 178° C. and finally over an iron at 407° C. at a rate of 42m/minute.

The individual filament titer was 0.36 dtex (DIN 53830) and the breakingforce, based on fineness, was 26 cN/tex at a breaking force elongationof 1.1% (DIN 53834, part 1).

The initial modulus was 28 N/tex. It was determined from the gradient ofthe stress-strain diagramat between 0.3 and 0.5 % elongation.

Comparison Example 1

Aromatic polyamide of 100 mol % of p-phenylenediamine and 100 mol % of2,5-furandicarboxylic acid chloride.

The polycondensation according to Example 1 was repeated, but with thedifference that a solution of 24.12 g of furandicarboxylic aciddichloride (0.125 mol) in 37 ml of N-methylpyrrolidone was used insteadof the solution of the mixture of furandicarboxylic acid dichloride andterephthalic acid dichloride. The intrinsic viscosity of the polymer wasonly 0.49.

Comparison Example 2

Aromatic polyamide of 100 mol % of p-phenylenediamine and 100 mol % of2,5-furandicarboxylic acid by direct polycondensation with triphenylphosphite and 3-methylpyridine.

12.98 g of p-phenylenediamine (0.120 mol), 19.27 g of furandicarboxylicacid (0.123 mol) and 82 g of triphenyl phosphite (0.264 mol) wereinitially introduced into a reaction vessel of 2 1 capacity. 134 g of2-methylpyridine (1.44 mol) and 600 ml of NMP, in which 9.2 g of lithiumchloride and 35 g of calcium chloride had been dissolved beforehand,were added under a nitrogen atmosphere. All the substances had beencarefully purified and dried beforehand. The mixture was heated at 90°C. for 35 hours, while stirring. After the resulting solution had beenobtained, it was stirred into 6 1 of 2% strength hydrochloric acid. Thepolymer which had precipitated was washed 4 times with water heated to70° C. and 3 times with acetone and dried in vacuo at 120° C. for 24hours. The intrinsic viscosity was only 0.33.

Comparison Example 3

Aromatic copolyamide of 100 mol % of p-phenylenediamine, 15 mol % of2,5-furandicarboxylic acid chloride and 85 mol % of terephthalic aciddichloride.

The polycondensation according to Example 1 was repeated with thedifference that 3.69 g of 2,5-furandicarboxylic acid chloride (0.019mol) and 21.60 g of terephthalic acid dichloride (0.016 mol) wereemployed. In contrast to Example 1, the reaction mixture did not form aclear solution but a yellow pasty slurry. After the temperature had beenincreased to 80° C., the amount of lithium chloride in the mixture wasincreased by 14.55 g (9.5% by weight in total, based on NMP). A slurryof undissolved material was then still present. The reaction mixture wasstirred into an excess of 2% strength hydrochloric acid. The resultingsolid was further treated as described under Example 1. Measurement ofthe intrinsic viscosity gave a value of only 0.2.

We claim:
 1. An aromatic copolyamide which has an intrinsic viscosity inthe range from 1.0 to 5.0 dl/g measured at 25° C. in NMP and which issoluble in organic solvents and which contains no hydroxyl groupsconsisting essentially of the recurring structural units (I), (II) and(III) ##STR11## to the extent of at least 90 mol % and 0 to 5 mol % ofend groups of the structural units (IV) ##STR12## in which the symbolsAr¹, Ar² and R¹ have the following meaning:Ar¹ is a divalent aromaticradical which is substituted by optionally one or two branched orunbranched C₁ to C₄ alkyl or alkoxy radicals, aryl or aryloxy radicalsor is unsubstituted and is optionally bridged by --SO₂ -- or --CO--, theamine groups being on non-adjacent ring carbon atoms; Ar² is a divalentaromatic radical which is substituted by optionally one or two branchedor unbranched C₁ --C₄ alkyl or C₁ --C₄ alkoxy radicals, aryl or aryloxyradicals or C₁ to C₆ perfluoroalkyl or perfluoroalkoxy radicals or byfluorine, chlorine, bromine or iodine or is unsubstituted in which Ar¹and Ar² are identical or different and independent of one another, andR¹ is an optionally halogen-substituted C₁ l to C₁₀ alkyl group or aradical of the structure (V) ##STR13## in which R² is hydrogen orhalogen or a branched or unbranched alkyl or alkoxy radical or an arylor aryloxy radical and the sum of the molar proportions of (II) and(III) to the molar proportion of (I) are in the ratio of 0.9:1 to 1.1:1,the molar proportions of (II) and (III) simultaneously being in a ratioto one another of 60:40 to 10:90.
 2. An aromatic copolyamide as claimedin claim 1, which contains units which are derived from terephthalicacid and/or isophthalic acid as structural unit II.
 3. An aromaticcopolyamide as claimed in claim 1, which contains units which arederived from a substituted or unsubstituted phenylenediamine asstructural unit I.
 4. A process for the preparation of an aromaticcopolyamide as claimed in claim 1, which comprises subjecting components(VI), (VII) and (VIII) ##STR14## which Ar¹ and Ar² have the meaninggiven in claim 1 and X is a chlorine atom or a hydroxyl group, topolycondensation with one another in an organic solvent at a temperaturein the range from -20° to 120° C., components (VII) and (VIII) being ina molar ratio to one another of 60:40 to 10:90 and the proportionthereof, based on the proportion of component (VI), being 90 to 110 mol%.
 5. The process as claimed in claim 4, wherein the terminal aminogroups of the aromatic copolyamide are neutralized by addition of amonocarboxylic acid chloride or anhydride of the formula (IX) ##STR15##in which Y is chlorine or a group --OC--R¹ and R¹ has the abovementionedmeaning.
 6. The process as claimed in claim 5, wherein themonocarboxylic acid chloride or anhydride of the formula (IX) is addedin a concentration in the range from 0 to 5 mol %, based on the aromaticcopolyamide.
 7. The process as claimed in claim 4, wherein a halide saltof a metal of the first and/or second group of the Periodic Table of theElements is added to the reaction solution to increase the solubility.8. The process as claimed in claim 4, wherein the organic solventemployed is one which contains amide bonds.
 9. The process as claimed inclaim 4, wherein an alkali metal oxide or hydroxide or alkaline earthmetal oxide or hydroxide or a compound of the formula (X), (XI) or (XII)##STR16## in which R⁴, R⁵, R⁶, R⁷ and R⁸ are identical or different andindependently of one another are hydrogen or a branched or unbranchedalkyl group, is added to the reaction solution as an acid-bindingadditive.
 10. The process as claimed in claim 9, wherein theacid-binding additive is added to a solution of (VI) in a polyamidesolvent and this solution is then subjected to polycondensation withcomponents (VII) and (VIII).
 11. The process as claimed in claim 4 or10, wherein an acid-binding additive, is added after the end of thepolycondensation.
 12. The process as claimed in claim 8, wherein theorganic solvent is dimethylacetamide, N-methyl-pyrrolidone, dimethylformamide or N-methylcaprolactam.
 13. The process as claimed in claim11, wherein the acid-binding additive is lithium hydroxide or calciumoxide.
 14. A shaped article or coating comprising a copolyamide asrecited in claim
 1. 15. A fiber, membrane or film comprising acopolyamide as recited in claim 1.